1. Field of the Invention
The present invention relates to an information processing device and method, and program, and specifically, relates to an information processing device and method, and program whereby a color gamut more suitable for image data to be processed can be provided.
2. Description of the Related Art
In recent years, there are more and a wider variety of digital image devices of which the color expression regions differ. In particular, color gamut expansion of image display devices is remarkable. The color gamut has been markedly expanded during the process from CRT (Cathode Ray Tube) displays, plasma displays, LCDs (Liquid Crystal Display), and further to organic Electro Luminescence Displays (OELD), for example. Heretofore, a workflow based on SRGB (standard RGB), which is the standard color space of existing PC monitors, has been proposed as a method for matching colors for output among devices having different color gamuts. However, a great number of imaging apparatuses, such as digital still cameras, video cameras, and so forth, which can image colors outside the SRGB color gamut, have come onto the scene.
Thus, with a system exchanging image data between devices which can handle various types of color gamut, there is a case where color gamut conversion of image data (compression or expansion, i.e., color matching) has to be performed. For example, in a case where an image of imaged wide color gamut image data is output at various types of color gamut device including a wide color gamut display, it is demanded to output a high chroma color outside the color gamut more naturally. Particularly, high-lightness and high-chroma colors have to be output smoothly while suppressing hue distortion, a phenomena wherein hue changes undesirably while chroma remains unchanged.
Therefore, there has been a method wherein information indicating the color gamut of image data to be exchanged between devices is exchanged along with image data thereof, and accordingly, color matching can be executed at each device.
For example, as shown in FIG. 1, in a case where image data is transmitted from a sending terminal (source) 1 to a receiving terminal (sink) 2, when the color gamuts (color expressible regions) of the sending terminal 1 and receiving terminal 2 differ from each other, color gamut conversion has to be performed. This color gamut conversion may be performed at either the sending terminal 1 or receiving terminal 2. For example, as shown in an arrow 3, an arrangement may be made wherein color gamut information 5 indicating the color gamut of the sending terminal 1 is supplied to the receiving terminal 2 along with image data, and color gamut conversion is performed at the receiving terminal 2. Also, as shown in an arrow 4, an arrangement may be made wherein the sending terminal 1 obtains color gamut information 6 indicating the color gamut of the receiving terminal 2 from the receiving terminal 2, and converts the color gamut of image data to transmit this.
Color gamut conversion is performed based on the difference of the two color gamuts of the color gamut of the transmission source device and the color gamut of the transmission destination device of image data. In the case of the example in FIG. 1, color gamut conversion is performed by employing both of the color gamut information 5 of the sending terminal 1 and the color gamut information 6 of the receiving terminal 2.
For example, as shown in FIG. 2, color gamut compression has to be performed upon a portion where the color gamut 11 of the sending terminal 1 is narrower than the color gamut 12 of the receiving terminal 2 (portion surrounded with a curve 13). In general, a color gamut is compressed by a method for changing chroma and lightness so as to conserve the hue thereof.
Upon color gamut compression not being performed, a color outside the color gamut of the receiving terminal 2 (e.g., a high chroma color) but within the gamut of the sending terminal 1 is expressed with the edge color of the color gamut of the receiving terminal forcibly (natural clip or simple clip). For example, as to a color gamut (RGB space) such as shown in FIG. 3A, the original data existing outside the color gamut thereof is expressed with a color gamut edge (clip data) such as shown in FIG. 3B. As a result thereof, a phenomenon occurs such as hue distortion, for example, wherein the color of an image where the sky is gradually dawning changes toward yellow or the like, and accordingly, there is a possibility that the image may become very unnatural visually.
Therefore, color gamut compression is performed so as to prevent occurrence of hue distortion. For example, International Publication WO1999/055074 (corresponding to U.S. Pat. No. 6,560,356) describes color gamut compression to prevent occurrence of hue distortion.
In general, a method is employed wherein an equal hue plane of which the hue is equal is set, the chroma and lightness of a color to be compressed are moved two-dimensionally along the equal hue plane thereof, and accordingly, the compression direction thereof is changed. For example, as shown in FIG. 4A, an equal hue plane 21 is set to an portion where a color gamut 12 is narrower than a color gamut 11, and as shown in FIG. 4B, the chroma and lightness of a color to be compressed are moved two-dimensionally along the equal hue plane 21 thereof, and accordingly, the compression direction is changed. The hue is not changed even at any position on an equal hue plane, whereby occurrence of hue distortion can be prevented by compressing a color gamut with such a method.
Therefore, in the event that a color gamut to be drawn on an equal hue plane can be readily expressed as a color gamut expression (format), this format can be regarded as a format to be readily employed for general color gamut compression. Various formats for specifying a color gamut have been proposed.